In the erection of certain kinds of buildings, such as hangars and halls, as well as in the erection of bridges there is a frequent need for steel trusses capable of spanning considerable distances and/or of supporting heavy loads. In many cases, especially in buildings, it is desirable or even necessary to design such steel trusses as generally rectangular frames including a pair of generally horizontally extending, longitudinal beams, an upper one and a lower one, which are interconnected at their respective ends by vertical posts and between their ends by a plurality of struts, i.e. members in compression, and ties, i.e. members in tension.
In order to combine maximum strength with minimum weight in the completed truss, the various members thereof must be joined together with great care and accuracy in a pattern, in which they interact as efficiently as possible in a manner to give mutual support and thus prevent distortion of the truss under the expected load. Experience has shown that the most economic and safe way of achieving this is to complete the entire truss in a factory and to transport it as a unit to the building site, where it is needed.
When there is a need for trusses, the spans of which exceed about 25 meters, it is common practice to divide them into shorter sections, which can be completed as separate units in the factory and then conveniently joined together end to end at the building site, such as by welding, riveting or bolting. This facilitates transportation and still leaves only a minor part of the assembly work to be carried out at the building site, as is desirable.
However, when the span of the truss and/or the load to be supported thereby are of such magnitudes that it will be necessary to use a truss height, i.e. the distance between the upper and lower horizontal members, exceeding about 4 meters, severe transportation problems are likely to arise, in particular when the transports have to be carried out by trucks on public roads or highways. These problems are frequently extremely expensive to overcome, if at all possible to solve, unless the truss can be divided into factory-made sections having not only a moderate length but also a height, which is sufficiently small to let the truss-loaded vehicle pass ordinary road obstructions, such as underpasses, bridges and the like, with acceptable clearance.